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WHAT HAS CHANGED

What has changed: Snowfall amounts were increased across southern Herkimer County and a winter weather advisory for lake effect snow was issued from 5 AM this morning through 7 AM Saturday. Additionally, snow showers/flurries added to the forecast, especially along and south of I-90, through early this morning.

KEY MESSAGES

1. Very cold temperatures tonight into early this morning with some high terrain areas dropping below zero.

2. Additional Lake Effect snowbands will impact portions of central/southern Herkimer County tonight through Friday night.

3. Below normal temperatures continue through the weekend with a few chances for light snow showers.

4. Trending warmer next week with a couple additional chances for light precipitation.

DISCUSSION

KEY MESSAGE 1...As of 1:30 AM EST...Temperatures range from the 10s in the Mid Hudson Valley to around 0 in portions of the southern ADKs where there are more breaks of clearing. With a very cold airmass in place and snowpack on the ground for most areas, lows are expected to range from single digits for valley areas to a few degrees below zero for some of the higher elevations. Winds have diminished substantially from yesterday, but with gusts still up to 5-10 mph wind chills could reach 5 to 10 below zero for some high terrain areas. While not reaching cold weather advisory criteria, it will still be a very chilly start to the morning Friday. Additionally, will mention that current radar shows some light snow showers/flurries tracking across the region, especially south of I-90. This is in response to an upper shortwave tracking north of the region and some slight enhancement to mid-level moisture. While only a coating at most is expected with these light snow showers/flurries through around sunrise, this is still an addition to the previous forecast.

KEY MESSAGE 2...Main adjustments that were made to the NBM with this forecast package were for the lake effect snow in the southwestern ADKs and western Mohawk Valley today and tonight. With a 985 mb sfc low to our northeast and high pressure to our S/SW, low-level flow is from the W to NW. 850 mb temps are around -15 to -16C, with Lake Ontario surface temps around +4C, resulting is plenty of lake-induced instability. BUFKIT forecast soundings suggest inversion heights between 750-700 mb this morning, but falling this evening and especially tonight. 850 mb winds are only around 30 kt, which should keep the heaviest lake effect snowfall closer to the lakeshore, but nevertheless should still allow for the lake band to reach into Herkimer County early this morning. The band is expected to drop south near the NYS thruway this morning or early this afternoon as low-level flow veers slightly more to the northwest. Snowfall rates look to reach 0.5 to 1" in the heaviest part of the band across southern Herkimer County, but only have a 10-20% chance of exceeding 1" per hour for a brief period this afternoon per the latest HREF. Snow will be very light and fluffy, as the best lift looks to intersect the DGZ. The band should then lift back north into central Herkimer County and weaken overnight tonight and flow becomes more westerly again, winds weaken, and inversion heights lower. By 12z Saturday, expecting some 3-5" amounts in western Herkimer County near or just north of the Thruway, so we opted to issue a winter weather advisory for lake effect snow. Some snow showers/flurries with this band may extend further into the Mohawk Valley this afternoon or evening, but accumulations further east from Herkimer County look very light. Elsewhere across the region, dry and continued cold weather expected through Friday night.

KEY MESSAGE 3...The next chance for a few light snow showers will come Saturday night into Sunday. A southern stream disturbance will slide south of our region, with a northern stream, moisture-starved shortwave potentially bringing a few light snow showers with a coating to perhaps an inch or two of snow for most areas. The snow showers should end SUnday morning, but this shortwave will bring a reinforcing shot of cold air. In fact, with surface high pressure building over the region Sunday night, diminishing winds, clearing skies, and existing snow cover should lead to very efficient radiational cooling conditions. We already went a few degrees below the NBM, and may need to adjust temperatures even lower over the coming days. Temperatures will likely drop into the single digits to around zero south of I-90, with temperatures in the negative single digits for most areas north of I-90, except in the ADKs where temperatures could reach 10-15 below zero.

KEY MESSAGE 3...While Monday looks quite chilly, it should be the last day with well-below normal temperatures. Zonal flow moving back over the eastern third of the country will allow for moderating temperatures, so Tuesday temperatures should be closer to normal with temperatures potentially climbing above normal Wednesday and Thursday. A few upper shortwaves embedded in the zonal flow aloft will bring some additional chances for light precip. The best chances look to be Monday PM/night and Tuesday PM into Wednesday. For the first system, any precip would likely be snow showers, but for the second system some rain could mix in as well. Precip amounts/accumulation look very light through at least the middle of next week, however.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18z/Sat...VFR conditions will continue at KALB/KPOU/KGFL through the upcoming TAF period. VFR cigs at KPSF will likely trend to MVFR tonight and linger into Saturday morning. Latest radar trends show limited inland extent of lake effect snow showers, so removed all mentions at KALB/KPSF. If a flurry were to reach these TAF sites, confidence is low on any visibility reductions. Westerly winds between 5-10 kt are expected through much of the period.

Outlook...

Saturday Night: Moderate Operational Impact. Chance of SHSN. Sunday: Low Operational Impact. NO SIG WX. Sunday Night: No Operational Impact. NO SIG WX. Monday: No Operational Impact. NO SIG WX. Monday Night: Low Operational Impact. Slight Chance of SHSN. Tuesday: Low Operational Impact. Slight Chance of SHRA...SHSN. Tuesday Night: Moderate Operational Impact. Chance of SHRA...SHSN. Wednesday: Moderate Operational Impact. Chance of SHRA.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...Winter Weather Advisory until 7 AM EST Saturday for NYZ038. MA...None. VT...None.